The present invention relates to a variable displacement pump applicable to, for instance, a hydraulic source that supplies a working oil to sliding parts of an internal combustion engine for a vehicle.
Japanese Patent Application Unexamined Publication No. 2011-111926 A discloses a variable displacement pump for use in an internal combustion engine for a vehicle. Briefly explained, the variable displacement pump includes a cam ring, a pair of springs disposed to apply a displacement force to the cam ring in a direction in which an eccentric amount of a central axis of the cam ring with respect to a rotation axis of a rotor is increased as a whole (hereinafter referred to as “an eccentric direction”), and a pair of control fluid chambers configured to apply a displacement force to the cam ring in a direction in which the eccentric amount of the central axis of the cam ring is reduced as a whole (hereinafter referred to as “a concentric direction”) by introducing same discharge fluid pressure into an inside of each of the control fluid chambers. The springs are arranged such that biasing forces thereof are exerted on the cam ring in directions opposed to each other. As the eccentric amount of the central axis of the cam ring is reduced, a load that is applied to the cam ring in the concentric direction is discontinuously and stepwise increased. With this construction, the variable displacement pump has a two-stage discharge fluid pressure characteristic in which a first predetermined fluid pressure is retained in a first rotation speed range and a second predetermined fluid pressure is retained in a second rotation speed range. The discharge fluid pressure characteristic is brought close to a required fluid pressure characteristic of the engine, so that useless energy consumption can be lowered.